In the production of oil from subsea oil fields, it is often necessary to use multiple wells. Some wells produce oil; others are used for gas or water injection to increase a field production rates. Some wells require workover to remove deposits while the balance of the field continues to flow and other wells may require testing to verify the benefit of production enhancement measures. It is therefore preferable to maintain flow path continuity from each well head to the production equipment and thus avoid mixing of fluid from multiple wells.
In present production systems for offshore oil production utilizing floating tankers or vessels, flexible piping and swivels are used to allow the vessel to rotate with the wind direction. Such rotation requirement places severe restraints on customary oil well activities necessary for oil production. Such prior proposed systems have included a fluid swivel having up to six independent flow paths passing therethrough, the swivel being attached to the vessel bow. An example of such a system is described in U.S. Pat. No. 4,254,523.
Another present system allows production from greater than six wells by utilizing undersea manifolds to group production from such multiple wells in up to six flow paths. This method may allow oil production from twenty or more wells, but the individual flow path from each well head to production equipment is lost by mixing the oils streams in the undersea manifold. Costs of fabrication and expense of maintenance of such an undersea manifold system is a disadvantage to this system.
Another prior proposed system for transporting production fluid to a single point moored vessel includes the use of a turret connected directly to the vessel or a single point mooring buoy connected to the vessel with an articulated yoke mechanism. In such instances, a multiple passage fluid swivel is utilized or a piping manifold is required in the mooring structure. An example of such a turret with a manifold system is shown in U.S. Pat. No. 3,525,312. Where a large number of subsea wells are to be produced, tested and remotely controlled from a floating tank or vessel, the prior proposed use of a fluid swivel and/or manifold becomes very complicated, heavy, expensive and is subject to high maintenance costs.
A prior proposed system for transferring production fluids to a floating vessel and utilizing flexible hose or riser lines is described in U.S. Pat. No. 3,366,088. Flow lines from a plurality of subsea wells are connected to an anchor means, the flow lines being combined at the anchor means for transfer of fluid to a limited number of flexible riser lines and thence to a float where the lines may be connected to tankers brought alongside the float. As the float weathervanes about the anchor, the plurality of flexible lines twist. Untwisting of the lines is accomplished by turning the vessel about the anchor point in the opposite direction to the twist by using tugs to maneuver the vessel about its anchor point.